1. Field of the Invention
This invention relates to cameras in which the light metering circuit and either the range finding circuit or the electric motor for driving motion of the lens are supplied with electrical power from the same source.
2. Description of the Prior Art
In conventional cameras it has been the common practice that the photographer, while aligning the camera with an object to be photographed, pushes down the shutter release button a first stroke, the light metering circuit is rendered operative with the display of the object brightness information, or the exposure value, i.e. shutter time, or aperture value, within the finder and/or on the camera housing, letting him known what setting the camera is adjusted to. The range finding circuit, too, simultaneously starts to operate, determining whether the plane of the object image just coincides with the film plane, or if it does not coincide it is shifted forward or rearward therefrom, which is also displayed as in-focus, near focus, or far focus, within the finder.
In conventional cameras of the character described above, however, focusing is automated by using an AF motor. When the electrical power source of the AF motor is common with that of the light metering circuit, because the actual voltage of the electrical power source is temporarily lowered by the rush current at the start of current supply to the AF motor, it often results that the output of the light metering circuit was lowered as the battery voltage lowered, or that noise entered the output of the light metering circuit.
Similarly, for the conventional camera which operates with selection of the auto-focus mode where the range finding circuit is energized, and the visual focus mode where the range finding circuit is unenergized so that the distance adjusting ring of the photographic lens is manually moved as in ordinary cameras, because the switching of the mode selector from the auto to the visual mode results in rush current flowing to the range finding circuit, when it occurs during light metering as the shutter button is held in the first stroke, the drawback was that the light metering circuit was badly influenced so that the displayed value was erroneous, or photographs of incorrect exposure were obtained.
With such drawbacks in mind, it is a first object of the present invention to prohibit automatic exposure from being performed based on that output of the light metering circuit which is obtained when the voltage of the electrical power source for the light metering circuit abruptly changes.
A second object of the invention is to prohibit the automatic exposure operation from being performed based on that light value which is obtained from the light metering circuit when the range finder circuit starts to be supplied with electrical power.
A third object of the invention is to prohibit the automatic exposure operation from being performed based on that light value which is obtained from the light metering circuit when a supply of electrical power to the electric motor for driving the lens starts.